SummaryScan sampling is a common technique used to quantify the activities of animals, including waterfowl. When large numbers are present, it is often impractical to record the activities of each individual, and sub-sampling is employed. We present a method for the design and analysis of scan sampling studies involving sub-sampling, based on an actual study of waterfowl activity on a waste stabilisation pond. The design we propose avoids subjectivity in the selection of individuals,is truly random rather than haphazard, and is adaptable to other situations. It allows for the population on each sampling occasion to be divided into separate strata with samples taken from each. The method of analysis addresses the statistical issues arising from such designs. In estimating the proportion of individuals engaged in an activity, it uses the information from observations in which some of the individuals are counted but their activities not recorded, and estimates the sampling variance introduced by sub-sampling. In comparing the mean proportions for different levels of a factor, such as time of day, the method uses restricted maximum likelihood (REML), an algorithm which can account for the sampling variance as well as for missing data. It is anticipated that the methods described